2. Cells Flashcards
(101 cards)
1
Q
What are distinguishing features of eukaryotic cells?
A
- Cytoplasm containing membrane-bound organelles
- So DNA enclosed in a nucleus
2
Q
Describe the general structure of eukaryotic cells
A
ANIMAL:
cell surface membrane
mitochondria
nucleus
ribosomes
rough ER
smooth ER
golgi apparatus
lysosome
PLANT:
all the same as animal cells
chloroplasts (plants & algae)
cell wall (plants, algae and fungi)
vacuole (plants)
3
Q
Describe the structure of the cell surface membrane
A
- Hydrophilic phosphate heads —> are attracted to water
- Hydrophobic fatty acid tails —> repressed from water
- Phospholipid bilayer, contains proteins spanning the membrane
4
Q
Describe the function of the cell surface membrane
A
- Selectively permeable —> enables control of passage of substances in and out of the cell
- Molecules/receptors/antigens on surface —> allow cell recognition/signalling
5
Q
Describe the structure of the nucleus
A
- Nuclear envelope (double membrane and has nuclear pores)
- Nucleoplasm
- Nucleolus (dense region)
- Protein/histone-bound linear DNA (chromatin = condensed, chromosome = highly condensed)
6
Q
Describe the function of the nucleus
A
- Holds/stores genetic information which codes for polypeptides (proteins)
- Site of DNA replication
- Site of transcription
- Nucleolus makes ribosomes/rRNA
7
Q
Describe the structure of a ribosome
A
- Made of ribosomal RNAand protein
- Not a membrane bound organelle
8
Q
Describe the function of a ribosome
A
Site of protein synthesis (translation)
9
Q
Describe the structure of rER and sER
A
both composed of a system of membranes, rER has ribosomes on the surface
10
Q
Describe the function of rER and sER
A
rER:
> ribosomes on the surface synthesise proteins
> proteins processed/folded/transported into rER
> proteins packaged into vesicles for transport, e.g to Golgi apparatus
sER:
> synthesises and processes lipids
> e.g cholesterol and steroid hormones
11
Q
Describe the structure of Golgi apparatus and Golgi vesicles
A
Apparatus - flattened membrane sacs
Vesicle - small membrane bound sac
12
Q
Describe the function of the Golgi apparatus
A
- Modifies protein, e.g adds carbohydrates to produce glycoproteins
- Modifies lipids, e.g adds carbohydrates to produce glycolipids
- Packages proteins/lipids into Golgi vesicles
- Produces lysosomes (a type of Golgi vesicle)
13
Q
Describe the function of Golgi vesicles
A
- Transport proteins/lipids to their required destination
- e.g moves to and fuses with cell-surface membrane
14
Q
Describe the structure of lysosomes
A
Membrane bound organelle which contains hydrolytic enzymes
15
Q
Describe the function of lysosomes
A
- Release hydrolytic enzymes (lysozymes)
- To break down/hydrolyse pathogens or worn-out cell components
16
Q
Describe the structure of mitochondria
A
- Outer membrane
- Folded inner membrane called cristae
- Mitochondrial matrix —> contains small 70s ribosomes and circular DNA
17
Q
Describe the function of mitochondria
A
- Site of aerobic respiration
- To produce ATP for energy release
- e.g for protein synthesis/vesicle movement/active transport
18
Q
Describe the structure of chloroplasts in plants and algae
A
- Double membrane
- Stroma —> contains thylakoid membrane, small 70s ribosomes, circular DNA and starch granules/lipid droplets
- Lamellae —> thylakoid linking grana
- Grana —> stacks of thylakoids
19
Q
Describe the function of chloroplasts in plants and algae
A
- Absorbs light energy for photosynthesis
- To produce organic substances, e.g carbohydrates/lipids
20
Q
Describe the structure of the cell wall in plants, algae and fungi
A
- Composed mainly of cellulose in plants/algae
- Composed of chitin (N2 containing polysaccharide) in fungi
21
Q
Describe the function of the cell wall in plants, algae and fungi
A
- Provides mechanical strength to the cell
- So prevents cell changing shape or bursting under pressure due to osmosis
22
Q
Describe the structure of the cell vacuole in plants
A
- Has a tonoplast membrane
- Contains cell sap
23
Q
Describe the function of the cell vacuole in plants
A
- Maintains turgor pressure in cell (stops plant wilting)
- Contains cell sap —> stores sugars, amino acids, pigment and any waste chemicals
24
Q
Describe how eukaryotic cells are organised in complex multicellular organisms
A
Tissue —> a group of specialised cells with a similar structure working together to perform a specific function, often with the same origin
Organ —> aggregations of tissues performing specific functions
Organ system —> group of organs working to perform specific functions
25
What are the distinguishing features of prokaryotic cells?
- Cytoplasm lacking membrane-bound organelles
- So genetic material not enclosed in a nucleus
26
Give 2 examples of prokaryotic organisms
Bacteria and archaea
27
Describe the general structure of prokaryotic cells
ALWAYS PRESENT:
> cell wall (contains murein- glycoprotein)
> cell-surface membrane
> cytoplasm
> small 70s ribosomes
> circular DNA (free in cytoplasm & not associated with proteins)
SOMETIMES PRESENT:
> flagella
> plasmids (small rings of DNA)
> capsule
28
Compare & contrast the structure of eukaryotic and prokaryotic cells
Eukaryotic V Prokaryotic
Membrane bound organelles <—> no membrane bound organelles
Has a nucleus (contains DNA) <—> No nucleus (DNA free in cytoplasm)
DNA is long and linear & associated with histone proteins <—> DNA is short and circular & not associated with proteins
Larger 80s ribosomes <—> smaller 70s ribosomes
Cell wall only in plants, algae and fungi (cellulose or chitin) <—> cell wall in all prokaryotes (murein)
Plasmids/capsule never present (sometimes flagella) <—> Plasmids, capsule and flagella sometimes present
Larger overall size <—> much smaller overall size
29
Explain why viruses are described as acellular and non-living
- Acellular —> not made of cells, no cell membrane/cytoplasm/organelles
- Non-living —> have no metabolism, cannot independently move/respire/replicate/excrete
30
Describe the general structure of a virus particle
1. Nucleic acids surrounded by a capsid (protein coat)
2. Attachment proteins allow attachment to specific host cells
3. No cytoplasm, ribosomes, cell wall, cell-surface membrane etc
4. Some also surrounded by a lipid envelope, e.g HIV
31
Describe the difference between magnification and resolution
Magnification = number of times greater the image is then the size of the real (actual) object
> M = I/A
Resolution = minimum distance apart 2 objects can be to be distinguished as seperate objects
32
What are the principles and limitations of optical microscopes? (8)
- Light focused using glass lenses
- Light passes through specimen, different structures absorb different amounts and wavelengths
- Generates a 2D image of a cross-section
- Low resolution due to long wavelength of light
- Can’t see internal structures of organelles or ribosomes
- Specimen must be thin
- Low magnification (x1500)
- Can view living specimens
- Simple preperation
- Can show colour images
33
What are the principles and limitations of transmission electron microscopes?
- Electrons focused using electromagnets
- Electrons pass through specimen, denser parts absorb more and appear darker
- Generates a 2D image of a cross-section
- Very high resolution due to short wavelength of electrons
- Can see internal structures of organelles and ribosomes
- High magnification (x1,000,000)
- Specimen must be very thin
- Can only view dead/dehydrates specimens as uses a vacuum
- Complex preperation so artefacts (dust, air bubbles) often present
- Does not show colour (black and white image)
34
What are the principles and limitations of scanning electron microscopes?
- Electrons focused using electromagnets
- Electrons deflected/bounce off specimen surface
- Generates a 3D image of surface
- High resolution due to short wavelength of electrons
- Specimen does not need to be thin
- High magnification (x1,000,000)
- Can’t see internal structures
- Can only view dead/dehydrated specimens as uses a vacuum
- Complex preperation so artefacts often present
- Does not show colour (black & white image)
35
List the steps in calculations involving magnification, real size and image size
1. Note formula & rearrange if necessary
2. Convert units if necessary
3. Calculate answer and check units required
36
How can you calculate magnification using a scale bar?
1. Measure scale bar image in mm
2. Convert to micrometers
3. Magnification = scale bar image / actual scale bar length (written underneath)
37
Describe how to convert between different units
m —> mm—> µm —> nm
Divide by 1000 each time
38
Describe how the size of an object viewed with an optical microscope can be measured
1. Line up (scale of) eyepiece graticule with (scale of) stage micrometer
2. Calibrate eyepiece graticule - use stage micrometer to calculate size of division on eyepiece graticule
3. Take stage micrometer away and use graticule to measure how many divisions make up the object
4. Calculate the size of the object by multiplying number of divisions by size of division
5. Recalibrate eyepiece graticule at different magnifications
39
Describe and explain the principles of cell fractionation and ultracentrifugation as used to seperate cell components
1. Homogenisation: use a blender —> disrupts cell membrane, breaking open cells and releasing contents/organelles
2. Place in an ice cold (to reduce enzyme activity —> so organelles not broken down/damaged), isotonic (so water doesn’t move in or out of organelles by osmosis —> so they don’t burst), buffered (to keep pH constant —> so enzymes don’t denature) solution.
3. Filter homogenate through a gauze —> remove large, unwanted debris e.g whole cells/connective tissue
4. Ultracentrifugation: separates organelles in order of density/mass
> centrifuge homogenate in a tube at a high speed
> remove pellet of heaviest organelle and respin supernatant at a higher speed
> repeat at increasing speeds until seperated out, each time pellet made of lighter organelles
(nuclei > chloroplasts/mitochondria > lysosomes > ER > ribosomes)
40
Describe the stages of the cell cycle in eukaryotic cells
1. INTERPHASE:
> S phase (DNA replicates semi-conservatively) —> leading to 2 identical copies joined at the centromere
> G1 (cell grows and receives a signal to divide) and G2 (number of organelles and volume of cytoplasm increases, protein synthesis - error checking of newly synthesised DNA)
2. MITOSIS:
> nucleus divides
> to produce 2 nuclei with identical copies of DNA produced by parent cell
3. CYTOKINESIS:
> cytoplasm and cell membrane divide
> to form 2 new genetically identical daughter cells
41
Describe the behaviour of chromosomes & role of spindle fibres in mitosis
Stage 1 - Prophase:
> chromosomes condense, becoming shorter/thicker (so visible) —> appear as 2 sister chromatids joined by a centromere
> nuclear envelope breaks down
> centrioles move to opposite pole of the cell forming a spindle network
Stage 2 - Metaphase:
> spindle fibres attach to chromosomes by their centromeres
> chromosomes align along equator
Stage 3 - Anaphase:
> spindle fibres shorten/contract
> centromere divides
> pulling chromatids (from each pair) to opposite poles of the cell
> requires energy in the form of ATP (provided by respiration in the mitochondria)
Stage 4 - Telophase:
> chromosomes uncoil, becoming longer and thinner
> nuclear envelope reforms = 2 nuclei
> spindle fibres/centrioles break down
42
Why do some eukaryotic cells not undergo the cell cycle?
- Within multicellular organisms, not all cells retain the ability to divide (e.g neurones)
- Only cells that do retain this ability go through a cell cycle
43
Explain the importance of mitosis in the life of an organism
Parent cell divides to produce 2 genetically identical daughter cells for …
1. Growth of multicellular organisms by increasing cell number
2. Replacing cells to repair damaged tissues
3. Asexual reproduction
44
Describe how tumours and cancers form
Mitosis is a controlled process
- Mutations in DNA/genes controlling mitosis can lead to uncontrolled cell division
- Tumour formed if this results in mass of abnormal cells
> malignant tumour = cancerous, can spread (metastasis)
> benign tumour = non-cancerous
45
Suggest how cancer treatments control rate of cell division
Some disrupt spindle fibre activity/formation
> so chromosomes can’t attach to spindle by their centromere
> so chromatids can’t be seperated to opposite poles (no anaphase)
> so prevents/slows mitosis
Some prevent DNA replication during interphase
> so can’t make 2 copies of each chromosomes (chromatids)
> so prevents/slows mitosis
46
Describe how prokaryotic cells replicate
Binary fission:
1. Replication of circular DNA
2. Replication of plasmids
3. Division of cytoplasm and cell wall reforms to produce 2 daughter cells:
> single copy of circular DNA
> variable number of plasmids
47
Describe how viruses replicate
Being non-living, viruses do not undergo cell division
1. Attachment proteins attach to complementary receptors on host cell
2. Inject viral nucleic acid (DNA/RNA) into host cell
3. Infected host cell replicates virus particles:
a) nucleic acid replicated
b) cell produces viral protein/capsid/enzymes
c) virus assembled then released
48
In which cells might cytokinesis not happen?
muscles cells as they have multiple nuclei
49
Describe how to set-up and use an optical microscope
1. Clip slide onto stage and turn on light
2. Select lowest power objective lens (usually x4)
3. a) use course focusing dial to move stage close to lens
b) turn course focusing dial to move stage away from lens until image comes into focus
4. Use fine focusing dial to get a clear image
5. Swap to a higher power objective lens, then refocus
50
What are the rules of a scientific drawing?
- look similar to the specimen/image
- no sketching/shading - only clear, continuous lines
- include a magnification scale (e.g x400)
- label with straight, uncrossed line
- use a sharp HB pencil
51
Explain how the stages of mitosis can be identified
In interphase chromosomes aren’t visible but nuclei are, in mitosis chromosomes are visible.
Prophase -
> chromosomes visible/distinct —> because condensing
> but randomly arranged —> no spindle fibre activity/not attached to spindle fibre
Metaphase -
> chromosomes lined up on equator —> because attaching to spindle
Anaphase -
> chromatids (in 2 groups) at poles of spindle
> chromatids V shaped —> because being pulled apart at their centromeres by spindle fibres
Telophase -
> chromosomes in 2 sets, one at each pole
52
What is a mitotic index?
- Proportion of cells undergoing mitosis (with visible chromosomes)
Mitotic index = number of cells undergoing mitosis / total number of cells in sample
53
Suggest how to calculate the time cells are in a certain phase of mitosis
1. Identify proportion of cells in named phase at any one time
> number of cells in that phase / total number of cells observed
2. Multiply by length of cell cycle
54
Describe the fluid-mosaic model of membrane structure
- Molecules free to move laterally in phospholipid bilayer
- Many components —> phospholipids, proteins, glycoproteins and glycolipids
55
Describe the arrangement of the components of a cell membrane
- Phospholipids form a bilayer (fatty acid tails face inwards and phosphate heads face outwards)
- Proteins
> intrinsic/integral proteins span bilayer e.g channel and carrier proteins
> extrinsic/peripheral proteins on surface of membrane
- Glycolipids (lipids with polysaccharide chains attached) found on exterior surface
- Glycoproteins (proteins with polysaccharide chains attached) found on exterior surface
- Cholesterol (sometimes present) —> bonds to phospholipid hydrophobic fatty acid tails
56
Explain the arrangement of phospholipids in a cell membrane
- Bilayer, with water present on either side
- Hydrophobic fatty acid tails repelled from water so point away from water/to interior
- Hydrophilic phosphate heads attracted to water so point to water
57
Explain the role of cholesterol in cell membranes
- Restricts movement of other molecules making up the membrane
- So decreases fluidity (and permeability) / increases rigidity
58
Suggest how cell membranes are adapted for other functions
- Phospholipid bilayer is fluid —> membrane can bend for vesicle formation/phagocytosis
- Glycoproteins/glycolipids act as receptors/antigens —> involved in cell signalling/recognition
59
Describe how movement across membranes occurs by simple diffusion
- Lipid soluble (non-polar) or very small substances e.g steroid hormones
- Move from an area of higher concentration to an area of lower concentration down a concentration gradient
- Across phospholipid bilayer
- Passive —> doesn’t require energy from ATP/respiration (only kinetic energy of substances)
60
Explain the limitations imposed by the nature of the phospholipid bilayer
- Restricts movement of water soluble (polar) & larger substances e.g Na+ / glucose
- Due to hydrophobic fatty acid tails in interior of bilayer
61
Describe how movement across membranes occurs by facilitated diffusion
- Water-soluble (polar) / slightly larger substances
- Move down a concentration gradient
- Through specific channel/carrier proteins
- Passive —> doesn’t require energy from ATP/respiration (only kinetic energy of substances)
62
Explain the role of carrier and channel proteins in facilitated diffusion
- Shape/charge of protein determines which substances move
- Channel proteins facilitate diffusion of water-soluble substances
> hydrophilic pore filled with water
> may be gated - can open or close
- Carrier proteins facilitate diffusion of slightly larger substances
> Complementary substance attaches to binding site
> Protein changes shape to transport substance
63
Describe how movement across membranes occurs by osmosis
- Water diffuses/moves
- From an area of high to low water potential/down a water potential gradient
- Through a partially permeable membrane
- Passive —> doesn’t require energy from ATP/respiration (only kinetic energy of substances)
64
What is water potential a measure of?
A measure of how likely water molecules are to move out of a solution
65
Describe how movement across membranes occurs by active transport
- Substances move from an area of lower to higher concentration / against a concentration gradient
- Requires hydrolysis of ATP and specific carrier proteins
66
Describe the role of carrier proteins and the importance of the hydrolysis of ATP in active transport
1. Complementary substance binds to specific carrier protein
2. ATP binds, hydrolysed to ADP + Pi, releasing energy
3. Carrier protein changes shape, releasing substance on side of higher concentration
4. Pi released —> proteins returns to original shape
67
Describe how movement across membranes occurs by co-transport
- 2 different substances bind to and move simultaneously via a co-transporter protein (carrier protein)
- Movement of one substance against its concentration gradient is often couple with the movement of another down its concentration gradient
68
Describe an example that illustrates co-transport
Absorption of sodium ions and glucose/amino acids by cells lining the ileum:
1. Na+ actively transported from the epithelial cells to blood (by Na+/K+ pump), establishing a concentration gradient of Na+ (higher in lumen than epithelial cell)
2. Na+ enters epithelial cell down its concentration gradient with glucose against its concentration gradient, via a co-transporter protein
3. Glucose moves down a concentration gradient into blood via facilitated diffusion
69
Describe the different factors that affect the rate of movement across cell membranes
- Increasing SA of membrane in increases rate of movement
- Increasing number of channel/carrier proteins increases rate of facilitated diffusion/active transport
- Increasing concentration gradient increases rate of simple/facilitated diffusion and osmosis
- Increasing concentration gradient increases rate of facilitated diffusion —> until number of channel/carrier proteins becomes a limiting factor as all saturated
- Increasing water potential gradient increases rate of osmosis
70
Explain the adaptations of some specialised cells in relation to the rate of transport across their internal and external membranes
- Membrane folded e.g microvilli in ileum —> increase in SA
- More protein channels/carriers —> for facilitated diffusion (or active transport - carrier proteins)
- Large number of mitochondria —> make more ATP by aerobic respiration for active transport
71
What is an antigen?
- Foreign molecule/protein/glycoprotein/glycolipid
- That stimulates an immune response leading to production of antibody
72
How are cells identified by the immune system?
- Each type of cell has specific molecules on it’s surface (cell-surface membrane/cell wall) that identify it
- Often proteins —> have a specific tertiary structure (or glycoproteins/glycolipids)
73
What types of cells and molecules can the immune system identify?
1. Pathogens (disease causing microorganisms) e.g viruses, fungi, bacteria
2. Cells from other organisms of the same species (e.g organ transplants)
3. Abnormal body cells e.g tumour cells or virus-infected cells
4. Toxins (poisons) released by some bacteria
74
Describe phagocytosis of pathogens
1. Phagocyte attracted by chemicals/recognises foreign antigens on pathogen
2. Phagocyte engulfs pathogen by surrounding it with it’s cell membrane
3. Pathogen contained in a vesicle/phagosomes in cytoplasm of phagocyte
4. Lysosome fuses with phagosome (forms phagolysosome) and releases lysozymes (hydrolytic enzymes)
5. Lysozymes hydrolyse/digest pathogen
75
What does phagocytosis lead to?
Leads to the presentation of antigens where antigens are displayed on the phagocyte cell-surface membrane, stimulating the specific immune response (cellular and humoral)
76
Describe the response of T-lymphocytes to a foreign antigen (cellular response)
Recognise antigens on surface of antigen-presenting cells, e.g infected cells, phagocytes presenting antigens, transplanted cells, tumour cells.
- Specific helper T cells with complementary receptors on cell surface bind to antigen on antigen-presenting cell —> activated and divide by mitosis to form clones which stimulate:
> cytotoxic T cells —> kill infected cells/tumour cells (produce perforin - embeds in cell-surface membrane and makes a pore so substances can enter or leave the cell)
> phagocytes —> engulf pathogens by phagocytosis
> specific B cells —> (humoral response)
> memory cells —> recognise specific antigen
77
Describe the response of B lymphocytes to a foreign antigen (humoral response)
Recognise free antigen e.g in blood or tissues, not just antigen presenting cells
1. Clonal selection:
> specific B lymphocyte with complementary receptor (antibody on surface) binds to antigen
> this is then stimulated by helper T cells (release cytokines)
> so divides rapidly by mitosis to form clones
2. Some differentiate into plasma cells —> secrete large amounts of (monoclonal) antibodies
3. Some differentiate into memory cells —> remain in the blood for a secondary immune response and divide by mitosis to make plasma cells if they re-encounter an antigen
78
What are antibodies?
- Quaternary structure proteins (4 polypeptide chains)
- Secreted by B lymphocytes e.g plasma cells in response to specific antigens
- Bind specifically to antigens forming antigen-antibody complexes
79
Describe the structure of an antibody
Y-shaped structure
- 2 light chains and 2 heavy chains
- 2 heavy chains and 2 light chains bound by disulphide bridges
- Constant regions at the bottom and variable regions near the top
- Antigen binding site at the top of variable region
80
Explain how antibodies lead to the destruction of pathogens
- Antibodies bind to antigens on pathogens forming an antigen-antibody complex
> specific tertiary structure so binding site/variable regions binds to complementary antigen
- Each antibody binds to 2 pathogens at a time causing agglutination of pathogens
- Antibodies attract phagocytes
- Phagocytes bind to the antibodies and phagocytose many pathogens at once
81
Explain the differences between the primary and secondary immune response
Primary —> first exposure to antigen
- antibodies produced slowly and at a lower concentration
- takes time for B plasma cells to be stimulated to produce specific antibodies
- memory cells produced
Secondary —> second exposure to antigen
- antibodies produced faster and at a higher concentration
- B memory cells rapidly undergo mitosis to produce many plasma cells which produce specific antibodies
82
What is a vaccine?
- Injection of antigens from dead or weakened pathogens (attenuated)
- Stimulating formation of memory cells
83
Explain how vaccines provide protection to individuals against disease
1. Specific B cells with complementary receptor binds to antigen
2. Specific T helper cells binds to antigen-presenting cell and stimulates B cell
3. B cell divides by mitosis to form clones
4. Some differentiate into plasma cells which release antibodies
5. Some differentiate into memory cells
6. On secondary exposure to antigen, memory cells rapidly divide by mitosis to produce B plasma cells
7. These release antibodies faster and at a higher concentration
84
Explain how vaccines provide protections for populations against disease
- Herd immunity —> large proportion of population vaccinated, reducing spread of pathogen
> large proportion of population immune so do not become ill from infection
> fewer infected people to pass pathogen on/unvaccinated people less likely to come in contact with someone with disease
85
Describe the differences between active and passive immunity
ACTIVE <—> PASSIVE
1. Initial exposure to antigen (e.g vaccine or primary infection) <—> no exposure to antigen
2. Memory cells involved <—> no memory cells involved
3. Antibody produced and secreted by plasma cells <—>antibody introduced from another organism e.g placenta
4. Slow, takes longer to develop <—> faster acting/immediate
5. Long term immunity as antibody can be produced in response to specific antigen again <—> short term immunity as antibody hydrolysed (endo/exo/dipeptidases)
86
Explain the effect of antigen variability on disease and disease prevention
- Antigens on pathogens change shape/tertiary structure due to gene mutations (creates new strains)
- So no longer immune (from vaccine or prior infection)
> memory cell receptors cannot bind to/recognise changed antigen on secondary exposure
> specific antibodies not complementary/cannot bind to changed antigen
e.g yearly flu vaccines, no HIV vaccine and catch a cold many times
87
Describe the structure of a HIV particle
- Lipid envelope
- Attachment proteins on surface
- Capsid
> containing viral RNA
> enzyme reverse transcriptase
88
Describe the replication of HIV in helper T cells
1. HIV attachment proteins attach to receptors on helper T cell
2. Lipid envelope fuses with cell-surface membrane, releasing capsid into cell
3. Capsid uncoats, releasing RNA and reverse transcriptase
4. Reverse transcriptase converts viral RNA into DNA
5. Viral DNA inserted/incorporated into helper T cell DNA
6. Viral protein/capsid/enzymes are produced
a) DNA transcribed into HIV mRNA
b) HIV mRNA translated into new HIV proteins
7. Virus particles assembled and released from cell (via budding)
89
Explain how HIV causes the symptoms of acquired immmune deficiency syndrome (AIDS)
- HIV infects and kills helper T cells (host cell) as it multiple rapidly
> so T helper cells cant stimulate cytotoxic T cells, B cells and phagocytes
> so plasma cells can’t release as many antibodies for agglutination and destruction of pathogens
- Immune system deteriorates —> more susceptible to infections
- Pathogens reproduce, release toxins and damage cells
90
Explain why antibiotics are ineffective against viruses
Viruses do not have structures/processes that antibiotics inhibits:
1. Viruses do not have metabolic processes (e.g do not make proteins)/ribosomes
2. Viruses do not have bacterial enzymes/murein cell wall
91
What is a monoclonal antibody?
- Antibody produced from genetically identical/cloned B cells/plasma cells
- So have the same tertiary structure
92
Explain how monoclonal antibodies can be used in medical treatments
- Monoclonal antibody has a specific tertiary structure/binding site/variable region
- Complementary to receptor/protein/antigen found only on a specific type of cell (e.g cancer cell)
- Therapeutic drug attached to antibody
- Antibody bind to specific cell, forming antigen-antibody complex, delivering drug
> some monoclonal antibodies can also block antigens/receptors on cells - prevents chemicals binding which enables uncontrolled cell division
93
Explain how monoclonal antibodies can be used in medical diagnosis
- Monoclonal antibody has a specific tertiary structure/binding site/variable region
- Complementary to specific receptor/protein/antigen associated with diagnosis
- Dye/stain/fluorescent marker attached to antibody
- Antibody binds to receptor/protein/antigen, forming an antigen-antibody complex
94
Explain the use of antibodies in the ELISA test to detect antigens - DIRECT
1. Attach sample with potential antigens to bottom of well
2. Add complementary monoclonal antibodies with enzymes attached —> bind to antigens if present
3. Wash well —> remove unbound antibodies (prevent false positive)
4. Add substrate —> enzymes create products that cause a colour change (positive result)
95
Explain the use of antibodies in the ELISA test to detect antigens - INDIRECT
1. Attach specific monoclonal antibodies to the bottom of the well
2. Add sample with potential antigens, then wash well (remove unbound antibody)
3. Add complementary monoclonal antibodies with enzymes attached —> bind to antigens if present
4. Wash well —> remove unbound antibodies (prevent a false positive)
5. Add substrate —> enzymes create products that cause a colour change (positive result)
96
Explain the use of antibodies in the ELISA test to detect antibodies
1. Attach specific antigens to bottom of well
2. Add sample with potential antibodies, wash well (remove unbound antibody)
3. Add complementary monoclonal antibodies with enzymes attached —> bind to antibodies if present
4. Wash well —> remove unbound antibody
5. Add substrate —> enzymes create products that cause a colour change (positive result)
97
Suggest the purpose of a control well in the ELISA test
- Compare to test to show only enzyme causes colour change
- Compare to test to show all unbound antibodies have been washed away
98
Discuss some general ethical issues associated with the use of vaccines and monoclonal antibodies
- Pre-clinical testing on/use of animals —> potential stress/harm/mistreatment
> but animals not killed & helps produce new drugs to reduce human suffering
- Clinical trials on humans —> potential harm/side effects
- Vaccines —> may continue high risk activities and still develop/pass on pathogen
- Use of drug —> potentially dangerous side effects
99
Suggest some points to consider when evaluating methodology relating to the use of vaccines and monoclonal antibodies
- Was the sample size large enough to be representative of the whole population?
- Were participants diverse in terms of age, sex, ethnicity, and health status?
- Were placebo/control groups used for comparison?
- Was the duration of the study long enough to show long-term side effects?
- Was the trial double-blind (neither doctor/patient knew who was given drug or placebo) to reduce bias?
100
Suggest some points to consider when evaluating evidence and data relating to the use of vaccines and monoclonal antibodies (results)
- What side effects were observed, and how frequently did they occur?
- Was a statistical test used to see if there was a significant difference between start and final results?
- Was the standard deviation of final results large, showing some people did not benefit?
- Did standard deviations of start and final results overlap, showing there may not be a significant difference?
- What dosage was optimum? Does increasing does increase effectiveness enough to justify extra cost?
- Was the cost of production & distribution low enough?
101
How does the ELISA test work for pregnancy tests?
1. Sample of urine is added
2. Mobile antibody, complementary in shape to the antigen being tested for and has a coloured dye attached
3. A second antibody complementary in shape to the antigen is immobilised further along - binds to antigen (already bound to coloured antibody) and causes a colour change
4. A third antibody is immobilised which is complementary in shape to the first antibody - always causes a colour change
2 lines = pregnant
